Hi,
Please have a look into the SET_XYZ and GET_V_XYZ of the fields.
SET_XYZ - This is used to set the data of the attribute from the UI to the BOL layer
Coming to your question , collection wrapper will be filled when we use set_property method of the entity.
e.g: lr_entity->set_property( iv_attr_name = 'corp.grp' iv_value = lv_value).
Please check it and let me know the queries if any.
Regards,
Karthik